While the amount of investment in IT levels off, the amount of data is increasing. It is, therefore, important to reduce the cost of storage systems.
For example, it is expected that a ServerSAN storage system, which is one of distributed storage systems and in which a large number of general-purpose servers are connected to each other via a network and generate a storage pool, will be widely used in the future. Especially, it is considered that the ServerSAN storage system is an effective solution in a system that is configured to execute high-performance analysis and in which high-speed SSDs are installed in server nodes for large big data analysis.
In addition, a storage system in which multiple storage devices (nodes) form a redundant array of inexpensive (or independent) disks (RAID) group and which provides a logical volume generated based on the RAID group to a higher-level device (for example, a host computer) is known.
In the storage system having a redundant configuration, the bit cost or capacity efficiency of the RAID group is determined based on the ratio of the number of data blocks forming the RAID group and the number of protective blocks (mirror blocks or parity blocks) for the redundancy. In a configuration of RAID5 or RAID6, the capacity efficiency of a RAID group, which has a stripe configuration with a number n of data blocks (D) and a number m of parity blocks (P) or is configured with nD+mP, is n/(n+m). For example, the capacity efficiency of a RAID group configured with 3D+1P (RAID5) is 3/(3+1)=75%.
As a background technique in this technical field, Patent Literature 1 discloses a method for building a reliable system while reducing read latency by appropriately distributing and placing write data in nodes in a ServerSAN storage system.
In addition, as another background technique in this technical field, Patent Literature 2 discloses a method for improving the capacity efficiency of a system by expanding an existing RAID group (for example, 3D+1P→4D+1P).